Variable focal length optical objective



June 12, 1962 T. l. HARRIS ETAL 3,038378 VARIABLE FOCAL LENGTH OPTICAL OBJECTIVE T @2 55 Filed Jan. 12, 1959 Ssneets-sheet 1 X ,Z 0 z5 @ww fm v X f) .2

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June 12, 1962 T. l. HARRIS Erm. 3,038,378

VARIABLE FOCAL LENGTH OPTICAL OBJECTIVE Filed Jan. 12, 1959 3 Sheets-Sheet 2 June 12, 1962 T. l. HARRIS ET AL VARIABLE FOCAL LENGTH OPTICAL OBJECTIVE Filed Jan. l2, 1959 Degrees of rototion of Zooming Ring 66 from Extreme Telephoto Position 3 Sheets-Sheet 3 rChange in oxiol separation1 of Lens group 3 from Lens qroup 4 os Zooming Ring 66 is Rototed from Extreme Telephoto Position `Change in oxiol seporotion of Lens group 2 from Lens' group 4 os Zooming Ring 66 is Rototed from Extreme Telephoto Position Inches of movement from Extreme Telephoto Position fzznZ/ons 772027205 Iffczrrals Pi/aler z/rfofuzs'orz jv group 1 is adjustable to focus from fthrefrfeet to innity United States Patent O 3,038,378 VARIABLE FOCAL LENGTH OPTICAL OBJECTIVE Thomas I. Harris and Walter J. Johnson, Mundelein, Ill.,

assignors to Bell & Howell Company, Chicago, Ill., a

corporation of Illinois Filed Jan. 12, 1959, Ser. No. 786,309 3 Claims. (Cl. 88-57) This invention relates to a variable focal length optical objective primarily intended for photographic use but applicable for general optical purposes as well.

An object of the invention is the provision of a new and improved zoom optical objective in which the focus of the objective may be rapidly adjusted through a wide range.

Another object of the invention is to provide an optical objective in which the equivalent focal length may be varied over a four to one range while maintaining a high degree of optical correction throughout the range and with very little change in back focal length.

A further object of the invention is to provide a zoom lens system in which both primary and higher order spherical aberration, coma, astigmatism, iield curvature, distortion and axial and lateral chromatic aberrations are highly corrected in all focal length adjustments and variation of distortion is minimized to not materially greater than one percent.

It is to be understood that `the terms front and rear as used herein refer to the ends of the objective respectively nearer the longer and shorter conjugates thereof.

In the accompanying drawings forming a part hereof:

FIG. 1 is a sectional View of an optical objective of the spherical type having a beam splitter and forming one embodiment of the invention adjusted for one equivalent focal length;

FIG. 2 is a sectional view of the objective shown in FIG. 1 adjusted to another equivalent focal length;

FIG. 3 is a sectional view of the objective shown in FIG. 1 adjusted to still another equivalent focal length;

FIG. 4 is a longitudinal sectional view of the objective shown in FIG. l showing a mechanical mounting and adjusting mechanism for the objective;

FIG. 5 is a sectional view of the optical objective shown in FIG. 1 but omitting the beam splitter; and

FIG. 6 is a graph illustrating movements of lens groups of the objective.

The invention provides a zoom lens objective comprising four components in which ythere is provided a rear component fixed relative to the image plane, a front com- 0 ponent and a second component immediately behind the front component is adjacent to and movable axially to the front component to provide change in magnification and a third component is positioned between the second component and the rear component and is adjustable in a non-linear manner. The front component may be adjusted to provide slight changes in focus to accommodate the objective for different object distances.

Referring to the drawings, the zoom optical objective shown therein includes a positive, spherical, front group of lenses or component 1, a negative, spherical, second group of lenses or component 2, a positive, spherical third group of lenses or component 3, and a posi iv fourthngroupgofdenseslzl'..@3132996924A The front lens The front lensgrouyis composed of lenses 1 o 1 having radii of curvatures of optical surfaces R1 to R1, thicknesses t1 to t1 and axial separations s1 and S11. The lenses L1 and L1 comprise a negative meniscus doublet and is shown as a cemented doublet thought it may be of the air separatedf edge con- ICC tact type if desired. The lens L3 is a positive singlet and the lens L1 is a positive meniscus singlet. The shapes of these lenses L1 to L1 are so chosen as to minimize coma and variation of distortion as well as higher order spherical aberration.

The negative second lens group 2 includes lenses L, to L8 having optical surfaces R8 to R14 with axial separations s1 :gid 15, and axial thicknesses t5 to t8. lens?- groupiis axially adjustable as a'tmit relative to ythe lens group 1 to vary the axial separation s3 by a lens mount 30 1 Gafllto vary the magnification of the objective. 1 The lens groups'compos'd'ft'ree'embrs the first of which is a cemented doublet formed by lenses L5 and L, whose cemented surface is largely responsible for the small variation of distortion. Following this doublet are the lenses L1 and L8, which are separated by a relatively long air space which reduces the coma and higher order spherical aberration. The lens L, is in edge contact with the lens L6. The lens L1 is shaped so that the variation of aperture aberrations of its surface substantially reduce the variations of aperture aberrations of the cemented surface of the cemented lenses L5 and L1.

The third lens group 3 includes lenses L9 and L10 forming a doublet which is shown as cemented but also may be of the air separated type. The lenses L9 and L11 have axial thicknesses t9 and r11, with Variable axial separations sLapd s, respectively bgmeep the component Th'" also is`iii'ciuded' beam splitter L`11wliichmayb`e omitted; 11

application Serial No. 780,026 filed December l2, 1958, by Walter I. Johnson and assi s the present application. for

ed tg thi same assi ee e beam splitter is provide if desired, and is disclosed and claimed in copending\ i ,1

p riding, is xed relative to the lens group 4, and is separated from the component 4 by axial separation S8. The beam splitter has plano optical slnfaces R18 and R19, and is positioned in a portion of the objective in which the rays are substantially collimated.

The rear lens group 4 is positive, and includes lenses L12 to L1B having radii of curvature of optical surfaces R211 to R117, axial thicknesses i12 -to r11; and axial separations S9 and S10. The lenses L12 and L13 are shown as a positive meniscus, cemented doublet, but may also be an air separated doublet. The lenses L15 and L15 also form a positive meniscus doublet and are shown in the cemented form but may be of the air separated type. The lens L11 is a biconvex singlet. The rear lens group 4 is fixed relative to the focal plane, and is a three member derivative of the Petzval type in which the last two members, comr posed of a singlet L1.,t and a doublet L11 and a doublet L15 and L16, correct the astigmatism, distortion, lateral color and oblique spherical aberration, while the first member L12 and L13 balances the spherical aberration, coma and axial color of the syste/m.

r 'J5 and 2 is varied manually to provide the change in magnitication while the separation between lens are fixed withgespect to the final image groups 2 and ,1' tf1 jzooming ens groupis moved ear 'iliefdf'tii 1n FIG. 1 while component 3 is moved in a nonlinear manner and with changing direction. Because lens group 2 in its median position is Working at approximately 1:1 conjugates, the movement of lens group 3 is small with respect to the movement of lens group 2. Focusing of the system for finite object distances may be accomplished by moving component 1 forward. During use, the component 1 is adjusted for a finite object distance and then the components 2 and 3 may be adjusted to vary magnification without change in back focal length.

plane during/,fl

In FIG. 4 of the drawings there is shown an adjustable mount 30. The mount 30 includes a casing 31 having a threaded bushing portion 32 adapted to be screwed into fixed position in a camera (not shown). The lenses L11, L15 and L16 are fixed in the casing by the bushing portion 32, a spacer bushing 33 and a retaining ring 34. The lenses L12 and L13 are fixed in the casing by a pinned insert 35, and are secured in the insert by a retaining ring 36. A diaphragm or stop 37 of the iris type positioned between the lenses L11 and L12 may be adjusted manually by a knurled ring 38 suitably marked, calibrated and mounted rotatably on the casing 31. The ring 38 is connected to an iris ring 39 by a pin 40 extending through a slot 41-in the casing 31. A spring-pressed ball detent 42 seating in one of slots 43 holds the stop 37 in adjusted position. A sleeve 51 is threaded into the front end of the casing 31 and has an insert 52 threaded thereinto and mounting the beam splitter L11. The insert 52 has cam slots 53 for pins 54 of the stop 37, and the insert 35 has holes 55 for pins 56 of the stop. An elongated sleeve-like guide 61 mounted slidably and rotatably in the sleeve 51 carries the lenses L9 and L19 fixedly thereon by means of a mounting ring 62 threaded thereinto, and'carries a lens mounting sleeve 63 slidably and rotatably therein. The sleeve 63 carries the lenses L5 to L9 fixedly therein by means of a spacer 64 and a locking ring 65.

To zoom or change magnification of the objective, a knurled zooming ring 66 is rotated manually on the sleeve 51 in guide rings 67, and turns the guide 61 therewith by means of a pin 68 fixed to the guide 61 and splined to the zooming ring 66 by a key 69 slidable in a longitudinal keyway 70 in the zooming ring. The pin carries a rotatable bearing sleeve 71, and projects through a cam slot 73 extending partially around the sleeve 51. As the zooming ring is turned from the position thereof shown in FIG. 4, in which the objective has an equivalent focal length of 76 mm., the guide 61 is first moved to the right, as viewed in FIG. 4, to move the lenses L9 and L10 to the right at a rate of speed non-linear relative to the rate of turning movement of the zooming ring 66 until the lenses L9 and L19 reach their farthest rghthand positions, in which positions they are adjusted for an equivalent focal length of 46 mm. Then, on continued turning of the zooming ring 66, the guide 61 with the lenses L9 and L19 are moved back to the left again at a non-linear rate of speed until, at the limit of travel of the zooming ring, the lenses L9 and L19 are at their extreme lefthand positions as shown in broken lines in FIG. 4, in which positions the lenses L9 and L19 are properly positioned for an equivalent focal length of 19 mm. of the objective. During the entire adjustment of the guide 61 and lenses L9 and L19 first to the right and then to the left, the lens mounting sleeve 63 is moved continuously to the left at a rate of speed linear with respect to the rate of turning of the zooming ring 66 to keep the component 2 in proper position at all positions of the component 3 for perfect focus of the objective. That is, as the component 2 is moved to change the magnification, the component 3 is moved non-linearly relative thereto to keep the objective always in focus at the film plane. The movement of the mounting sleeve 63 is effected by a cam slot 81 in the guide 61 and a pin 82 which is fixed to the sleeve 63 and splined to the sleeve 51 by a key 83 slidable in keyway 84. The cam slot 81 is so shaped to compensate for the non-linearity of the movement of the guide 61 and make the movement of the sleeve 63 linear relative to the xed outer sleeve `51.

An end sleeve is fixed to the sleeve 51 by a set screw 89, and a lens mounting barrel 87 carrying the lens group 1 by means of spacers 90 and 91 and a locking ring 92 is manually adjustable therein by multiple pitch thread segments 93 to adjust the component 1 for any equivalent focal length of the objective between 3 feet and innity. The barrel 87 is rotated by means of a focusing ring 94 keyed to the barrel. To prevent accidental removal of the barrel during focusing movement of the lens group 1, an overhanging lip 96 of a collar 95 projects inwardly beyond a shoulder 97 of the barrel 87. This limits the short focus adjustment. To precisely provide for focusing for infinity, an adjustment screw 98 threaded through a bore 99 in the ring 94 is set at the factory, and engages the collar to limit movement of the component 1 to the right to the position shown in the drawing in which the objective is focused at infinity.

The axial movements of the lens groups 2 and 3 relative to the lens group 4 are illustrated in the chart or graph of FIG. 6. The lens group 2 moves linearly away from the extreme long equivalent focal length or telephoto position to the extreme wide angle position while the lens group 3 initially moves closer to the lens group 4 and then away from the lens group 4 in accordance with the curve shown in FIG. 6. The ordinate of the graph shown in FIG. 6 represents degrees of movement of zooming ring 66 from the extreme telephoto adjustment.

In the preferred form of this invention, the equivalent focal length or magnification may be varied over a 4:1 range, maintaining a high degree of optical correction over the f/ 1.9 aperture throughout the range. Specifically, spherical aberration (both third and higher order), coma, astigmatism, field curvature, distortion, and axial and lateral color are more highly corrected in all focal length positions than in other lenses of this type. Variation of distortion is not materially greater than one percent. 1

Specifically, with reference to the equivalent focal lengths f1, fz, f3 and f4 of the respective components 1, 2, 3 and 4, the radii must conform to the following:

1 1 1 ra-5m =.3319 (Fig. 1) Telephoto 1 1 1 a =.1075 (Fig. 2) Mean 5f R17 3f3 =.8007 (Fig. 3) Wide angle 1 1 1 R1g= 2f4 R20 -7f4 5 L RFQ :F100 nd=12o v=6o.3

sa =.10O l l O Rw=+1.707 3 o 7f4 R21 gf Lu Rn= 1500 tu=. 00 11d-1.580 V-41. 1 l 1 L13 3 l13=.150 71d=1.751 V=27.7

10 R21-+13. 61 n 700 41,4 R22 2f* Rn=+a.4s9

l l 1 L R 4001 t14=.200 nd=1.620 V=60.3 24= s 1j- 1223 f4 R25=+1`422 S10 .300 1 1 1 15 L15 Ru- 890 15=A60 7ld=1.520 V=60.3 f4 R24 4L La RFHUO m .120 77d 1.751 v 27.7

The obJective shown 1n FIG. 5 1s 1dent1cal with that O 0 l 20 shown in FIGS. 1 to 4 except that the objective shown in -3f4 Rza f4 FIG. 5 does not include the beam splitter L11 of the viewnder, an o tically separate viewfinder of known con- 1 1 P 0 R 15f struction (not shown) being used therewith. Also, the

21 5 spacing sq-i-s between the lenses L10 and L12 of the ob- It t d d th t th al f th. t. 2 jective of FIG. 5 is different to compensate for the relstln enf e ah gener scope sth 1S mven lotn moval of the lens L11 and may be either shorter or longer. cover ose odmsw erem one or more o e componen S A preferred example of the objective shown in FIG. 5 arcomlounde b d. f h b. t. h is constructed in compliance with the following table in pr? erre em o ment 9 t .e o Jec we s (,.wn m which the component 1 is adjusted for focus of infinity, FIG. 1 1s constructed substantlally 1n accordance W1th the 30 dimensions are in terms of inches L1 to L10 and L12 to follryvmfablgm which. the compfolienltl 1 s flocuse tflr L16 are the lenses, R1 to R1, and R20 to R27 the respective m .It/1 mflenolns mi? mdterms ot.mc es Va ms o e radii of curvature of the surfaces, t1 to 110 and tw to tls the equlv ent oc engt. an sep'flra loris s3 S6 an s" cof' axial thicknesses, s1 to sm the axial separations, nd the respond to the respecmfe Zoqmmg aqlustments shown. m indices of refraction for the sodium D line and V the IG' 1 aand land mdwchAtgeuihces 9E refraclon 35 Abbe dispersion numbers, and in which values of the or e so .mnll d .ne and e d Sliferslon num ers equivalent focal length and separations s3, s7-s8 are given are respectlve y eslgnate as "d an for the two extremes and an intermediate adjustment of the ob'ective: fl=3.4158 f1=-.9025 =3.3670 fi=1.72s5 J 40 fr=3.4158 f2=.9025 f3=3.3670 f.=1.7285 2.967 (Fig. 1) flephnto f all th 6493 2 967 Telephoto Equwalentfocanength I gig: Wieafgcll o eng Equivalent foca11ength={1l lgi focal 1engrh=493 Relative Aperture=fl1-9 R1 =-2.96o 45 R1 =2.960 L1 i t1 =.150 7ld=1.720 V=29-3 L1 f1 =.150 7Zd=1 720 V=29.3

Ri =+15.3s93 =+15.3s93 L, R 3 3485 t: =.420 77d=1.020 V=60.3 R 3 3 8 t) =.420 F1620 V=60.3

31 =.014 3 Si :.014 R4 =+5,2225 Ri =+5.2225 L, R 20008 t: =.320 77a=1.700 V=47.8 50 L1 R 20 008 :a =.320 nd=1.700 V=47.s s n =.o14 5 s2 =.o14 Ro =+2A00 Rs =I2.400 L4 f4 .320 72d=120 V=60.3 L4 4 =.320 7ld=1.620 V=60.3

=1.6791 (Fig. 1) Telephoto 55 1.6791 Telephoto sa =1.1394 (Fig. 2) Mean sa 1.1394 Mean .0670 (Fig. 3) Wide angle .0670 Wide angle RB =+1.925 Rs =+1.925 L5 R t5=.200 nd=1.751 V=27.7 L5 R t=.200 nd=1.751 V=27.7

Le R 5720 z. =.0so nd=117 v=55.0 60 L. R 5720 t@ =.oso F1617 v=55 0 lo* a4=.160 ms4=.160 R11=2.280 R11=2.280 L7 R 336 1=.080 1ld=1.700 V=41.1 L1 R +1336 t1=.080 nd==1.700 V=41.1

1. nu 477 85 :A00 Ru +1 7 s :A00

1. .47 La Rn +2960 ta =.160 nd=1.720 V=29.3 La R13 +2960 tg =,160 nd=1.720 V=29.3

.1349 (Fig. 1) Telephoto .1349 Telephoto .9 .8990 (Fig. 2) Mean .1 .8990 Mean =1.2782 (Fig. 3) Wide angle 70 1.2782 Wide angle l ze =.100 nd=1.7oo V=47.s L. l t, 1oo F1700 v=29.a R14=+L336 R1a=+1.338 R 2 500 l10=.250 71d=1.517 V=4.5 L10 R 2 500 t1n=.250 7ld=1.517 V=64.5

While the invention is thus described, it is not to be limited to the precise details described, as changes may be readily made without departing from the spirit of the invention.

What is claimed is:

l. An optical objective of the zoom type comprising a positive front component; a negative second component positioned to the rear of the front component and axially adjustable to vary the magnification of the objective; a positive third component positioned to the rear of the second component and adjustable relative to the rst and second components; a fixed positive rear component; said front component comprising a front cemented meniscus doublet, an intermediate singlet and a rear singlet; said second component comprising a front cemented meniscus doublet, an intermedi-ate singlet and a rear positive meniscus singlet; said third component comprising a cemented doublet; said rear component comprising a front cemented meniscus doublet, an intermediate positive singlet and a rear cemented meniscus doublet; and further characterized in that said objective complies with the following limits in which f1 to f4 are the equivalent focal lengths of the front, second, third and rear components respectively, and beginning with the front end of the objective R1=to R27 designate the radii of curvature of the optical surfaces:

Kai n;

1 1 raffle,

1 1 (KR-'251m 2. An optical objective of the zioom type comprising a positive front lens group; a negative second lens group positioned to the rear of the front lens group and axially adjustable to vary the magnication of the objective; a positive third lens group positioned to the rear of the second lens group and adjustable relative to the first and second lens groups; a fixed positive rear lens group; and a beam splitter between the third and rear components; said front lens group comprising a front cemented doublet, and intermediate singlet and a rear singlet; said second lens group comprising a front cemented doublet, an inter mediate singlet and a rear singlet; said third lens group comprising a cemented doublet; said rear lens group comprising a front cemented doublet, an intermediate positive singlet and a rear cemented doublet; and further characterized in that said objective complies substantially with the following table in which the dimensions are in terms of inches, and beginning with the front end of the objective L, to L, designate the lenses, R1 to R27 the radii of curvature of the surfaces, t1 to tm the axial thicknesses, s1 `to sm the axial separations, nd the refractive indices for the D line, and V the Abbe dispersion numbers, and in which corresponding values in the order listed are provided for the equivalent focal length, s3, s, and sf, for adjustment, an intermediate adjustment and the other extreme adjustment of the second and third lens groups:

2.967 Telephoto Equivalent focal length: 1.479 Mean back focal length=.493

.741 Wide angle =1.6791 Telephoto sa =1.1394 Mean .0670 Wide angle Rs =-|1.925 La l5 =.200 ndr-*1.751 V=27.7

Rn La la =.O80 nd=l.6l7 V=55.0

s4 =.160 R1i=2.280 L1 is =.0S0 7ld=1.700 V=41.1

ss =.400 R13=+1A77 Ls is =.l60 7ld=1.702 V=29.3

=.1349 Telephoto as =.8990 Mean =.2782 Wide angle R15=+3.025 La t =.100 nd=1.700 V=47.8

R1s=+1.336 L10 t1n=.250 71d=l.5l7 V=64.5

=.3319 Telephoto s1 =.1075 Mean =.8007 Wide angle R1S= m tn=.400 7ld=l.620 V=60.3 Ri= ss =.100 Rzo=|1.707

1t=.300 7la=1.580 V=4l.0 Rz1=1.500

i1a=.150 lld=1.751 V=27.7 R2z=+13.361

Se =.700. R2a=+3A89 L14 l14=.200 lld=l.620 V=60.3

81=.300 Rz5=+1.422 L15 tnv-'.460 7ld=1.620 V=60.3

Rzs=z890 Lic i1n=.120 l.1=1.751 V=27,7

3. An optical objective of the zoom type comprising a positive front lens group; a negative second lens group positioned to the rear of the front lens group and axially adjustable to vary the magnification of the objective; a positive third lens group positioned to the rear of the second lens group and adjustable relative to the rst and second lens groups; a xed positive rear lensgrou d a beam s lufthansa thef. @new seltsamen.`

mglens group comprising a front cemented doublet, an intermediate singlet and a rear singlet; said second lens group comprising a front cemented doublet, an intermediate singlet and a rear singlet; said third lens group comprising a cemented doublet; said rear lens group comprising a front cemented doublet, and intermediate positive singlet and a. rear cemented doublet, and further characterized in that said objective complies substantially with the following table in which the dimensions are in terms of inches and beginning with the front end of the objective L1 to L18 designate the lenses, R1 -to R2, the radii of curvature of the surfaces, t1 to tu, the axial thicknesses, s1 to sm the axial separations, nd the refractive indices for the sodium D line, and V the Abbe dispersion numbers, and in which the upper values of the equivalent focal length, s3, ss and s7+s5 correspond to one extreme adjustment of the second and third lens groups, the middle values correspond to an intermediate adjustment and the lower values correspond to the other extreme adjustment:

Equivalent focal length={ 2.967 Telephoto 1.479 Mean beck focal length=.6493

.741 Wide angle R1 =2.960 L1 l =.150 71d=1,720 V=29 3 R1 =+15.3893 L1 l: =.420 nd=l.620 V=60.3

H1 ==.014 R4 =|5.2225 L; la =.320 71d=1.700 V=47.8

sz =.014 Ra =+8.400 L4 i4 =.320 77d=1.620 V=60.3

{1.6791 Telephoto 83 1.1394 Mean .0670 Wide angle Rs =+L925 L5 ls =.200 ttf-1.751 V=27.7

R9 eo L| te =.080 1ld=1.617 V=55.0

.n =.160 R11=2.280 L1 1 ==.080 71d=l.700 V=41.1

as =.400 R13=+1A77 La 2s =.160 Il1=1.720 V=29.3

.1349 Telephoto sa .8990 Mean 1.2782 Wide angle Ris=+3.025 La t1 =.100 7ld=1.700 V=47 8 R1|=+L336 L10 i1u=.250 71d=l.517 V=64.5

.6788 Telephoto arl-as .4544 Mean 1.1476 Wide angle Rm=+1.707 L11 i11=.300 lld=1.580 V=41.0

Rz1=1.500 L13 t1s=.150 7Ld=1.751 V=27.7

sa ==.700 R13=I3A89 L14 14=.200 1ld=1.620 V=60.3

t1s=A60 nd=1.620 V=60.3 Rzs=.890

iis=.120 7ld=1.751 V=27.7 R11=+4.170

References Cited in the le of this patent UNITED STATES PATENTS 2,649,025 Cook Aug. 18, 1843 2,718,817 Back et al Sept. 27, 1955 2,843,016 Reiss July l5, 1958 2,847,907 Angenieux Aug. 19, 1958 2,859,654 Back NOV. 11, 1958 2,906,172 Klemt Sept. 29, 1959 FOREIGN PATENTS 26,896 France Sept. Z8, 1860 1,120,271 France Oct. 14, 1957 1,123,471 France June 1l, 1956 

